My parents don’t allow me to drink raw water. What’s the “ghost” hidden in it?

Water is the source of life. It maintains body fluid balance, regulates body temperature, promotes digestion and metabolism, lubricates joints and tissues, helps excrete waste and toxins, maintains skin health, and affects mood and cognitive ability. According to the "Dietary Guidelines for Chinese Residents 2022", adults should drink 1500-1700 mL of water every day [1]. If water is so important, why did my parents never let me drink water directly from the tap? They said it contained bacteria and that drinking raw water would cause stomach pain. What exactly is hidden in drinking water?

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1. Microorganisms in drinking water

Drinking water may contain a wide variety of microorganisms, including bacteria, viruses, parasites, and many of them are harmful to the human body. If they multiply in large numbers under suitable conditions, they will cause drinking water contamination. Once consumed, they may cause intestinal dysfunction, vomiting, diarrhea, and other symptoms. In severe cases, they may even cause life-threatening waterborne diseases such as cholera, typhoid fever, and hepatitis A [2].

2. Importance of microbial indicators

In order to ensure the safety of drinking water, my country's "Standard for Drinking Water Quality" (GB5749-2022) promulgated in 2022 clearly stipulates the microbial indicators in drinking water [3]. These indicators include total colony count, total coliform group, Escherichia coli, etc. These indicators do not mean that only these bacteria are contained in drinking water, but are indicator bacteria that reflect the pollution level of drinking water.

2.1 Total colony count: This is an indicator for evaluating the cleanliness and purification effect of water quality [4]. Simply put, the total bacterial count is the total number of bacterial colonies grown in each gram or milliliter of sample under specific conditions. The higher the total colony count, or even if it exceeds the standard, it may mean that the water quality is polluted. my country's drinking water hygiene standards stipulate that the total colony count in every 1ml of drinking water cannot exceed 100 CFU/ml [3]. This CFU is a colony forming unit, which can be understood as not a bacterium but a bacterial community, which is a group of bacteria formed by multiple passages of bacteria on a counting plate.

2.2 Total coliform bacteria: Total coliform bacteria mainly come from human and livestock feces, as well as water and soil contaminated by feces. When total coliform bacteria are detected, it indicates that the water body may be contaminated by feces and there is a risk of intestinal infectious diseases spreading. my country's drinking water hygiene standards stipulate that total coliform bacteria should not be detected in every 100 ml of drinking water [3].

2.3 Escherichia coli: Also known as Escherichia coli, it is a common intestinal bacterium that can cause varying degrees of symptoms, such as fever, abdominal pain, diarrhea, nausea, vomiting, etc. [5]. my country's drinking water hygiene standards also stipulate that Escherichia coli must not be detected in every 100 ml of drinking water [3].

2.4 Giardia lamblia Giardia lamblia is a single-cell protozoan that mainly parasitizes the human small intestine and causes diarrhea. It is mainly transmitted through water and food contaminated by cysts. my country's drinking water hygiene standards stipulate that the number of Giardia lamblia is less than 1/10L[3].

2.5 Cryptosporidium Cryptosporidium is also a single-cell protozoan that mainly parasitizes the brush border of epithelial cells in the gastrointestinal tract of humans and other hosts. It is an important opportunistic pathogen that can cause diarrhea in humans and animals[6]. It is mainly transmitted through water sources contaminated with oocysts, mainly through fecal-oral and hand-oral routes. my country's drinking water hygiene standards stipulate that the number of Cryptosporidium is less than 1/10L[3].

3. Detection and control of microbial indicators

In order to ensure the safety of drinking water, it is necessary to conduct regular testing of microbial indicators in drinking water. Commonly used methods in laboratories include multi-tube fermentation method and membrane filtration method. Through testing, water quality problems can be discovered in time and corresponding treatment measures can be taken. In addition to testing, drinking water also needs to be treated as necessary to kill or remove microorganisms in the water. Common treatment methods include chemical disinfection, boiling, ultraviolet radiation and filtration.

4. Precautions

In order to ensure the safety of drinking water, the protection of water sources is also very important. In recent years, local governments have formulated a series of measures to protect drinking water sources, such as prohibiting the construction of poultry and livestock farms in water source protection areas, strengthening industrial waste management, prohibiting enterprises from discharging pollutants indiscriminately, and raising public environmental awareness and participation. In addition, water plants should also improve water quality treatment technology and strengthen the management of water supply systems to ensure the cleanliness of water leaving the plant.

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In daily life, we need to pay attention to drinking boiled water, because after high temperature, the protein structure of bacteria and viruses is destroyed, and the biological activity and pathogenicity are lost accordingly. Giardia lamblia and Cryptosporidium cannot survive in the process of high temperature heating. It is a simple and effective way to kill most bacteria and viruses. However, it is necessary to avoid long-term storage; regularly clean water storage equipment such as thermos at home; water purification equipment at home needs to be cleaned, disinfected and filter cartridges replaced regularly; develop good personal hygiene habits to prevent waterborne enteric infectious diseases.

References:

[1] China Nutrition Society, Dietary Guidelines for Chinese Residents[Z], China, People’s Medical Publishing House, 2023.

[2] Zhao Yu. Common diseases and prevention after earthquakes[J]. Science Friend, 2008(7):1. DOI:CNKI:SUN:KXZY.0.2008-07-053.

[3] “Sanitary Standard for Drinking Water” (GB5749-2022) [s]. Beijing: State Administration for Market Regulation, National Standardization Administration, 2022

[4] Cheng Yarou, Drinking Water Quality Testing and Health Risk Assessment in Guiyang City[D], Master's thesis of Guizhou Normal University, 2015-05-26;11-12

[5]. Li Fan, Xu Zhikai. Medical Microbiology 9th Edition[M]. Beijing: People's Medical Publishing House, 2018: 102-106,108.

[6] Wang Yu; Jiang Shan; Wu Ning, Analysis of factors affecting the recovery rate of spiked insects[J]; Industry and Technology Forum. 2015, 14 (04); 47-48

Source: Chongqing Science Writers Association

Author: Wang Demiao, chief technician, Du Wenjing, deputy chief technician, Chongqing Shapingba District Center for Disease Control and Prevention; Zou Jingbo, chief technician, Chen Li, chief technician, Chongqing Yongchuan District Center for Disease Control and Prevention

Audit expert: Li Hanbin

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